Wound care treatments have evolved to comprise a complex range of strategies, devices and products. These include the application of topical medicated or anti-microbial solutions, medicated and non-medicated, occlusive and non-occlusive, adherent and non-adherent dressings. In general the healing of open wounds occurs most favouably when there is absence of infection and the healing takes place in a moist environment. Healing occurs by a series and sequence of cell-cell and cell-matrix interactions and involves the formation of new tissues. The choice of a particular wound management and dressing strategy is in principle dictated by the phase of healing and factors which affect the rate of healing such as anatomical site, medical-co-morbidity, age, infection etc. At this time the most commonly used antimicrobial agent used in topical wound care is silver. The major concern with silver is that there is an almost direct correlation between antimicrobial effect and cytotoxic effect on cells involved in healing wounds.
Silver in its ionic state possesses a very broad spectrum of antimicrobial efficacy. Particularly, ionized silver has broad antibacterial, antifungal and antiviral properties which are caused by the reactivity of silver ions with a variety of functional groups. Silver ions, similar to most heavy metals in their ionized state, can complex with electron-donating functional groups containing sulfur, oxygen or nitrogen. In biological systems these electron donor groups are present as functional groups such as thiols, carboxylates, phosphates, hydroxyl, amines, imidazoles and indoles, either singly or in many varied combinations. These electron donor groups are found in great numbers in a variety of biomolecules which make up microbes. The binding of ionized silver to any of these electron donor groups causes disruption or inactivation of the biological system, resulting in the microbe's death. Depending on the source of the silver ions, studies indicate that silver ions kill the microbe either by attacking the cell wall and membrane producing blebs or by producing aggregation of nuclear material into filaments
As a result, a silver or silver ion containing substance has been developed to improve conventional dressings.
A specific advantage of using a silver ion as a bacteriostatic agent is the general lack of the formation of bacterial tolerance to the compound. This is in contrast to many types of antibiotics. However a major drawback when using ionic silver for bacteriostatic purposes is the reduction of the ion to free silver which results in dark stainings. Such stainings have been reported to give potentially permanent pigmentation of the skin, which is so-called argyria.
U.S. Pat. No. 5,744,11 to Capelli discloses a “host-guest” relationship between silver ions and acyclic polyethers is accomplished through the use of excess of halide ions to keep the silver ions stable. U.S. Pat. No. 5,429,819 has disclosed a photo-stable composition comprising a complex of a silver ion and a thiosulphate salt carried on a porous particulate carrier.
The benefits of a moist healing environment have been well established but how to achieve this has been a challenge in product design. On strategy is to use occlusive dressings but another is to use a hydrating dressings. Hydrogels are of particular interest as potential hydrating dressings. They comprise a range of materials and include a permanent, three dimensional network of hydrophilic polymers; water fills the space between the polymer chains. They are available as gels, sheets and gels pre-applied to gauze. The amorphous gels are used for cavity wounds whilst sheet dressings and in pregnated gauze can be applied to surface wounds.
U.S. Pat. No. 4,871,490 discloses a sheet hydrogel dressing which is useful in keeping a wound moist but it does not have any inherent antimicrobial activity.
Thus there is to date no successful combination of a hydrogel dressing and silver ions in treating a wound. Further, there have been no reports that silver is used in a dressing in a film form.
It is known in the art TiO2 in an ultra-fine powder form is a photocatalytic antimicrobial agent. However, the prior art has not taught or suggested using TiO2 in a dressing as the antimicrobial agent.
The present invention is intended to provide a dressing which comprises a hydrogel base containing TiO2 in combination with silver ions.